Sheet metal products, in particular made of sheet steel, that vary in thickness and material quality are seeing increasing use in automotive production. It is thus possible to reduce the weight of body parts in line with their function. Body parts of this kind include, for example, A-, B-, and C pillars, bumpers and their cross members, roof frames, side impact beams, vehicle body shells, etc.
In this context, the prior art technique is to use so-called tailored blanks. These are blanks that are welded together out of a plurality of pieces of sheet metal with the same or different sheet thicknesses and material qualities. It is also possible to use so-called patchwork blanks. These are sheets of varying thicknesses and material qualities that are placed parallel to one another.
In the latter process, the sheets are placed onto one another and then joined to one another, in particular by means of spot welding.
Patchwork blanks have the disadvantage that the spot welded connections are subjected to powerful stresses during the shaping and can possibly also fracture. In addition, the gap that is present between the sheet metal layers can lead to corrosion problems that require a costly sealing to control. In addition, the transition between the individual thickness regions is relatively abrupt in both tailored blanks and patchwork blanks. As a result, when stress is exerted, undesirable stress concentrations can occur in the immediate transition region.
Although tailored and patchwork blanks do in fact permit achievement of a significant weight reduction, the corrosion protection is relatively costly.
DE 10 2009 052 210 B4 has disclosed a method for producing components out of sheet steel with regions of different ductility; a sheet metal blank composed of a hardenable steel alloy is either used to produce a component by means of deep drawing and the deep-drawn component is then at least partially austenitized by means of a heat treatment and then quench hardened in a tool or the blank is at least partially austenitized by means of a heat treatment and shaped in a hot state and is quench hardened then or thereafter; the sheet metal blank has a zinc-based cathodic corrosion protection coating; in regions of a desired higher ductility of the component, at least one other sheet is placed against the blank so that during the heat treatment, the blank is heated less in this region than in the remaining region.
The object of the invention is to create a method for producing partially hardened components out of hardenable sheet steel in which the coating of the sheet steel is not damaged or is only insignificantly damaged and a uniform hardness or ductility progression over the desired region is achieved while exerting as little stress as possible on the cooling element.
Another object of the invention is to create a method for producing partially hardened components out of hardenable sheet steel in which the risk of damage to the components on the one hand and/or to the cooling element and/or to the furnace support is minimized by facilitating the removal of and the ability to position the components.
Another object of the invention is to create a device for carrying out the method, which can be reliably used to provide ductile regions without damaging the surface of the steel component.